The invention relates to a wooden beam having sections which are subjected to transverse tension, which are reinforced by rod-shaped elements which are positioned to extend essentially transversely to its longitudinal direction.
Especially at through-holes in the span of such wooden beams, or else in the vicinity of their ends, if cut-outs are provided in the vicinity of the superposition region, there arise exceptional stresses due to forces which act transversely to the grain orientation, so that in those areas tears and cracks can form in the wooden beam parallel to the grain orientation.
It has already been proposed to insert, precisely in those sections of wooden beams subjected to transverse tension, rod-shaped elements for special reinforcement. In general, these rod-shaped elements were glued into pre-drilled holes. This yielded a certain amount of beam strengthening transversely to its longitudinal direction, i.e. transversely to the grain orientation.
In this regard, the premise is that the drill holes provided for the insertion of the rod-shaped elements heretofore normally extended over the entire height of a beam, or were provided at least starting at the top or at the bottom of the beam until well beyond the section that was actually subjected to transverse tension. On the one hand, this causes a corresponding consumption of time for creating the drill hole, for inserting the rod-shaped element and for gluing it in, and on the other hand, there results an exceptional consumption of materials through correspondingly long rod-shaped elements and a correspondingly large required quantity of adhesive.
The present invention has as its objective to substantially improve the reinforcement possibilities for a beam of the initially described variety in the region of sections subjected to transverse tension.
This is accomplished in accordance with the invention by forming the rod-shaped elements of screws which are provided with threaded segments at both of their end regions, which extend over a zone subjected to transverse tension, which are screwed in from the top or the bottom of the beam, which extend only over a portion of the height of the beam and which are therefore associated directly with the zone that is subjected to transverse tension.
Through these inventive measures, it has become possible to utilize relatively short screws instead of the prior, very long rod-shaped elements. Absorption of the tension forces is carried out solely by the threaded portions, which are engaged in the wood of the beam.
By means of the invention, there has been created the possibility, in practice, to utilize a screw for the present purpose, which is inserted appropriately deeply and is therefore located where corresponding transverse tension forces occur. This is advantageous especially for exceptionally tall wood beams. Such beams can have a height of one meter or more, but reinforcement due to the prevailing transverse tension is needed only over a predetermined segment of the beam height.
A preferred embodiment is one in which the screws extend approximately equally far above and below a zone of increased transverse tension. This ensures that the thread portions which are present at both ends of the screw provide adequate anchoring to essentially equal degrees, so that the transverse tension forces can be absorbed without any problems. However, such an arrangement becomes possible only if the screws can be screwed into the wooden beam less deeply or even more deeply, as appropriate.
In this connection, it is preferred that the length of the screws be chosen shorter than one half the height of the beam. Especially for beams of exceptional height this yields a very substantial saving of material and furthermore, especially when using screws with threaded sections, there occurs the lowest possible insertion turning moment. Such screws can be screwed into the wood beam without predrilling a hole, which also makes possible an appropriately deep insertion.
Especially in a wood beam of relatively great height, there occur in certain regionsxe2x80x94for example in the middle region of a curved beamxe2x80x94several sections subjected to transverse tension, and this can affect layers in all regions relative to the height of the beam. In such a case, the inventive technique can also be used advantageously, namely by screwing into sections subjected to transverse tension two or more screws spaced apart and approximately parallel to each other and axially displaced over the height of the beam. Thus, a relatively large segment of a beam can be provided with exceptional transverse tension reinforcement, namely through the screwing in of a multiplicity of screws which are screwed in from the top or the bottom side of the beam and in so doing are screwed in more or less far.
A preferred embodiment provides that the screws are equipped with a thread over their entire shaft length. This ensures that the screws can engage the wood of the beam over their whole length and are therefore capable of absorbing relatively high transverse tension forces.
It is further proposed that the screws have an internal tool drive at their one end, with the diameter of the segment of the screws which surrounds this internal tool drive being made approximately equal to or only slightly greater than the outer diameter of the thread. In this way, it becomes possible to screw the screw in relatively deeply without significant increase of the screwing-in moment and without damage to the threaded region inside the wood. In this way, it also becomes possible to screw the screws in very deeply so as to bring them to just that point where the sections subjected to transverse tension are present.
A preferred and very simple procedure for screwing the screws into the wood beam exists if the screws are screwed in with a screwdriver bit having a shaft adjoining the screw-engaging region, or an imaginary cylinder enclosing the shaft, which has a diameter that is equal to or smaller than the diameter of the portion of the screw which surrounds the internal tool drive and which has a length sufficient to bridge the region of the height of the beam from the internal tool drive of the screw all the way to the upper or lower limit, and beyond to the screwdriver engagement point. Thus, by use of a relatively long screwdriver bit the screws can be screwed to the desired depth into the wood beam. Without requiring pre-drilling, there is therefore created the possibility to place the screw at the appropriate location relative to the height of the beam.